Is it possible to inject thin wall PS cups, without nitrogen accumulators in the machine? Problem: Cavities do not fill completely.

it is possible to inject with full electric machines. The only issue is the shot size. With today technology in electric drives, injection machines are limited in injection speed & shot size; or injection time.

Valve gate hotrunner,good venting,stable core,l/t ratio below 400,barrel capacity in between 40-70/As well the injection profile need to be adjust,the initial speed shall not push the core tilt and change the thickness and bring hesitation and imbalance cavities

I would recommend measuring the wall thickness on oposing sides of the cup. I would suggest that core deflection is causing wall variation in the cup. The wall variation chokes off the flow path of the melt resulting in biased flow and corresponding shorts in the side of the cup with thinnest walls. Design of the mold and correct process parameters will minimize core deflection.

Accumulators give your rapid fill rates and the relative viscosity of the material is low which reduces pressure build up in the mold. You can increase barrel temps to the high ends of resin specifications to ease but not eliminate flow issues

is it possible to see the digital pictures of the part? Was the same mold running on the machine or its a first time run?

another practical way would be to add some addities for material flow increase. Also increas the temprature of melt and then inject. If it fills well and proper then you can go into re-engineering as to why it does not fills in normal circumstances. It could be any of the reason, core deflection, lesser traper at turning points, machine under capacity to fill thin walls and so on. A logical step by step; one by one analysis would pin point the problem, which may be one or multiples.

I go with curt is this case.
to further assit you the following: the flow lenght/wall ticknes are the main factors for yes or no for N2 accumulators. the venting is form extreem importancy for Ps burns easely. the machine must have an constant speed. in the case of an hotrunner the optimalisation of gating, temperature is very important.

succes

In support of Anton's question he is asking what we need to know. Flow length, Wall thickness, venting, runner design, gate design, cooling line layout etc. Once all of this has been reviewed then you can make an intellegent decision. Venting is super important. You need to give us all of this info to properly respond to your question.